We report theoretically on the dynamics of two vertical-cavity surface-emitting lasers (VCSELs) coupled unidirectionally through their optical fields, in the context of chaos synchronization and its use for chaos secure communications. One of the two VCSELs is rendered chaotic by optical feedback effects and injects its chaotic output into a second, slave VCSEL. Two different injection schemes are analyzed. A first configuration is such that the master VCSEL injects light polarized orthogonal to that emitted by the free-running slave VCSEL. The orthogonal optical injection induces polarization switching of the slave VCSEL, leading to polarization synchronization between master and slave. A second configuration considers a polarization-preserving optical injection. We report on anticipative and isochronous polarization synchronization and interestingly, we show that VCSEL polarization mode competition enhances the synchronization quality.